| Length | 245 m |
| Width | 162 m |
| Height | 19 m |
| Thickness of the roof | 9.20 m |
| Number of pens | 11 |
| Number of afloat pens | 4 (Pen n°1 to 4) |
| Number of dry docks | 7 (Pen n°5 to 11) |
| Surface | 43 000 m2 |
| Concrete used for building the base | 600 000 m3 |
Some pictures of the roof and the "fangrost" protection structure.
The port of Bordeaux had been used by the Kriegsmarine since June 1940 and quickly became the home port of Italian submarines. Far away from the main European front lines, this port had a strategic location for the Germans. Facing the Atlantic ocean, this port will house the majority of long range u-boats during the World War II.
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On the beginning of July 1940, the Italian and German headquarters decided to use the port of Bordeaux to establish a shared submarine base. In August of that year, Admiral Angelo Parona arrived from Italy with his staff. He named the new base "Betasom", beta being the Greek first letter of "Bordeaux" and Som the abbreviation of "sommergibili" Italian word, which means submarine.
A few weeks later, the first submarines arrived: they belong to the "11th Gruppo Italiano del Fero Subaequeo in Atlantico. This group is particularly powerful. After the Malaspina, the Dandolo, the Marconi and Finzi, not less than 23 other submarines reached Betasom between September and November 1940.
The efficiency of Italian submarines was much lower than Germans. Thus, during the trial period from October 10 to November 30, 1940, each Italian submarine sank an average of 20 tonnes per day against 1115 tonnes for a U-boat. This is due to several reasons : the Italians were not familiar with the "hunting playgrounds" of the Atlantic and they had less powerful submarines than their allies. Their submarines were not only slower on surface, but suffered alse a serious handicap : they had to wait 60 seconds before diving, which is huge in case of emergency.
The bulding of the protective bunker started In September 1941, to protect the submarines from the bombings. On october 1942, Bordeaux beacame the home base of the 12th German flotilla and the u-boat bunker became operationnal on january 17, 1943 when the U-178 entered the bunker for refit.
